#### Answer

He can't remove the first set of parenthesis if there is a negative sign in front of it. Also, he distributed incorrectly in the second part of the problem.

#### Work Step by Step

When there is a negative sign in front of parenthesis, you can remove the parenthesis by distributing -1 to the terms inside of the parenthesis. Therefore, $-(x+y)=-x-y$. Also, he didn't distribute the 3 correctly. $3(x-4y)=3x-12y$. The correct answer is $-x-y+3x-12y=2x-13y$.